A vehicle lamp includes a plurality of lamps for a high beam and a low beam. In recent years, there lamps adopt semiconductor light sources such as a Light Emitting Diode (LED) and a Laser Diode (LD). FIG. 1 is a circuit diagram of a vehicle lamp using a semiconductor light source.
A vehicle lamp 1r includes a light source 10 and a lighting circuit 20r thereof. The lighting circuit 20r includes a current source 30, a plurality of bypass switches 40_1 to 40_N, and a controller 50. The current source 30 receives a battery voltage VBAT (also referred to as an input voltage VIN) from a battery 2 via a switch 4 and stabilizes a drive current IDRV flowing through the light source 10 to a certain target amount.
The plurality of bypass switches 40_1 to 40_N are associated with a plurality of light emitting units 12_1 to 12_N, and ON/OFF of each bypass switch 40 can be controlled individually. When the i-th bypass switch 40_i is in an ON state, the drive current IDRV flows to the bypass switch 40_i instead of the light emitting unit 12_i, so that the light emitting unit 12_i is turned off. When the bypass switch 40_i is in an OFF state, the drive current IDRV flows to the light emitting unit 12_i, so that the light emitting unit 12_i is turned on. JP-A-2014-017463 discloses an example of a lighting circuit.
The inventors of the present invention has analyzed the vehicle lamp 1r of FIG. 1 and found the followings.
The light source 10 and the lighting circuit 20r are connected via wiring (harnesses). When a failure (for example, a ground fault) occurs at a point of the wiring, some or all of the light emitting units cannot be turned on. As an example, when an OUT1 pin is shorted to ground, all the light emitting units 12_1 to 12_N cannot be turned on, and when an OUT2 pin is shorted to ground, the light emitting units 12_2 to 12_N in the downstream cannot be turned on.
The present invention has been made in view of the above circumstances, and an exemplary object of the present invention is to provide a lighting circuit capable of reducing functional losses in a failure or an abnormal state.
According to an aspect of the present invention, there is provided a lighting circuit configured to drive a light source including a plurality of light emitting units connected in series. The lighting circuit includes a converter which is configured to supply a drive current to a light source, a plurality of high-side switches, and a plurality of low-side switches. Each high-side switch is provided between one end of a corresponding light emitting unit and one output of the converter. Each low-side switch is provided between another end of the corresponding light emitting unit and another output of the converter.
According to this aspect, the ON/OFF state of the plurality of light emitting units can be controlled by controlling states of the high-side switches and the low-side switches. Further, at the time of a failure, a failure part can be separated, and the lighting of the remaining light emitting units can be maintained. In the present specification, the failure may include a temporary abnormality.
The another output of the converter may be grounded and each low-side switch may be provided between the another end of the corresponding light emitting unit and the ground.
The lighting circuit may further include a diode provided between respective adjacent light emitting units. Accordingly, reverse flow of current can be prevented.
The lighting circuit may further include a plurality of monitoring circuits, each of which is configured to monitor an electrical state of one end of a corresponding light emitting unit. Accordingly, the failure can be detected.
Each monitoring circuit may monitor a voltage at one end of the corresponding light emitting unit. Accordingly, a short-circuit failure such as a ground fault or a power failure or an open circuit (disconnection) can be detected.
According to another aspect of the present invention, there is provided a vehicle lamp. The vehicle lamp may include the light source including the plurality of light emitting units connected in series and the above-described lighting circuit which is configured to drive the light source.
Incidentally, any combination of the above configuration elements, and the configuration elements and expressions of the present invention may be implemented as methods, devices, systems, or the like which are also effective as aspects of the present invention.
According to the above configuration, functional losses at the time of failure can be reduced.